The invention relates to a manufacturing process for splittable elastane multifilament yarns whereby coalescence of the individual filaments forming the yarn due to fusion, sticking or mechanical entangling or plying is prevented. The individual filaments obtainable from the process can be split after take-off the multifilament yarn bobbin and be further processed separately in textile production processes.
Elastane fibers are fibers consisting of segmented polyurethanes in at least 85% by weight. Their typical property spectrum is the result of using polyurethane-polyureas from oligomeric polyester- or polyether-diols, aromatic diisocyanates and short-chain aliphatic diamines. Filament formation is customarily effected by spinning solutions of the polyurethanes by the wet spinning process or preferably by the dry spinning process, suitable solvents in both cases being polar solvents such as dimethyl sulphoxide, N-methylpyrrolidone, dimethylformamide or preferably dimethylacetamide.
Commercial elastane yarns are well known. Owing to their elastic properties they are used for manufacturing functionalized textile products, i.e. articles exhibiting a combination of extensibility and retractive or shaping power. For this, the elastane filament yarn is combined, for example by overwrapping, overspinning or interlacing, with other inelastic yarns to form combination yarns, or the elastane filament yarn is knitted up directly with inelastic yarn.
It order that these processing operations may proceed without problems, the elastane yarns have to be virtually free of fluff, thin places and defects. The prior art teaches that the elastane yarns are produced as coalesced multifilament yarns. This means that the individual filaments forming the overall yarns are virtually stuck together during spinning, for example in the dry spinning process. A process for producing coalesce elastane yarns is described for example in U.S. Pat. No. 3,094,374 and European Patent Application 182,615. The former expressly describes the advantages of a multifilament with high interfilamentary adhesion with regard to consistent processing and discloses methods for achieving this property spectrum.
It was therefore not to be expected that elastane multifilament yarns having good processing properties could be obtained if the process used for producing them is deliberately geared to minimize or eliminate interfilamentary adhesion.
Laid-Open Document JP 03-059 112 describes bundled polyurethane multifilaments or monofilaments which are wound up on a bobbin in an oriented manner so that the bundled multi- or monofilaments require 15 mg or less for separation from the bobbin. They are further processed as separate multifilaments or monofilaments at a speed of at least 150 m/min. These products are obtained by subjecting the dry-spun filaments to cooling below 60xc2x0 C. and additionally adding a metal soap to the product. It is immaterial for the process of JP 03-059 112 whether multi- or monofilaments are separated.
It is an object of the present invention to produce multifilament yarns which are splittable into their individual filaments on unwinding from the bobbin. These individual filaments must not be mutually plied, entangled, or locally or longitudinally stuck together. The problem is to completely suppress such rare effects which occur every several hundred meters.
This object is achieved by a manufacturing process for producing splittable elastane multifilament yarns from conventional polyurethane-polyureas by means of a modified dry spinning process, which is characterized by the steps of
1) deploying in the spinning head of a conventional dry spinning apparatus one or more multihole spinning jets whose individual capillaries are located on one plate, the distance x between capillaries on one plate and the distance y between capillaries on adjacent multihole spinning jet plates conforming to the following relationship:
40 mm less than x less than y less than 500 mm, 
2) laminarizing the spinning gas flow in the dry spinning apparatus to prevent entangling of the individual filaments from one multihole jet and from adjacent multihole jets,
3) passing the resulting elastane yarns leaving the spinning shaft through a first thread guide with one opening per individual filament and then through a second thread guide which gathers a plurality of individual filaments together to form a multifilament, and
4) winding up the multifilament yarn.
The polyurea-polyurethanes are prepared by methods known per se. An advantangeous method is the synthesis of the fiber raw materials by the prepolymer process, in which, in a first step, a long-chain diol is reacted, in a solvent or in the melt, with a diisocyanate to form a prepolymer so that the reaction product contains isocyanate end groups (NCO groups).
Preferred long-chain diols are polyesterdiols on the one hand and polyetherdiols on the other. It is also possible to choose mixtures of the two kinds of diols. These generally have a number average molecular weight of 1000-6000.
Suitable polyesterdiols are for example dicarboxylic acid polyesters which may contain not only a plurality of different alcohols but also different carboxylic acids. Of particular suitability are copolyesters of adipic acid, hexanediol and neopentylglycol in a molar ratio of 1:0.7:0.43. Suitable polyesters have a molecular weight of 1000-4000.
Suitable polyetherdiols are for example polytetramethylene oxide diols, preferably with a molecular weight of 1000-000 (all stated molecular weights are number averages, unless otherwise indicated).
It is also possible to use polyester- and/or polyether-diols in combination with diols which contain tertiary amino groups. Particularly suitable are for example N-alkyl-N,N-bishydroxyalkylamines. Examples are the compounds:
4-tert-butyl-4-azaheptane-2,6-diol, -methyl-4-azaheptane-2,6-diol, -ethyl-3-azapentane-1,5-diol, -ethyl-2-dimethylaminoethyl-1,3-propanediol, -tert-pentyl4-azaheptane-1,6-diol, 3-cyclohexyl-3-azapentane-1,5-diol, 3-methyl-3-azapentane-1,5-diol, 3-tert-butylmethyl-3-azapentane-1,5-diol and 3-tert-pentyl-3-azapentane-1,5-diol.
The elastane raw materials are synthesized using the customary aromatic diisocyanates in admixture with small proportions of aliphatic and/or cycloaliphatic diisocyanates, if desired. Particularly good results are obtained with the following diisocyanates:
2,4-toluylene diisocyanate and also corresponding isomer mixtures, and
4,4xe2x80x2-diphenylmethane diisocyanate (MDI) or corresponding isomer mixtures. It is of course possible to use mixtures of aromatic diisocyanates.
Another form of the synthesis of elastane raw materials comprises mixing polyester- and polyether-polyurethane prepolymer and then reacting in a conventional manner to form polyurea-polyurethanes. The mixing ratio of polyester- and polyether-diols advantageous for the particular technical purpose is easily determined in preliminary experiments.
In the polyurea-polyurethane synthesis, the urea groups are introduced into the macromolecules by a chain-extending reaction. Customarily, the prepolymers (xe2x80x9cmacrodiisocyanatesxe2x80x9d) synthesized in the prepolymer stage to contain NCO end groups are reacted with diamines in solution. Suitable diamines are for example ethylenediamine, tetramethylenediamine, 1,3-cyclohexanediamine, isophoronediamine and also mixtures thereof. By using a small amount of monoamines, for example diethylamine or dibutylamine, during the chain extension, it is possible to achieve the molecular weight desired for the polyurea-polyurethanes. The chain extension itself can be carried out batchwise or continuously and with or without the use of CO2 as retarder.
A mixture of polyester- and polyether-polyurethane-ureas can also be formed following completion of the synthesis of the individual components.
The reactions are customarily carried out in an inert polar solvent, such as dimethylformamide or dimethylacetamide.
The polymer solution intended for spinning may additionally include a whole series of customary additives, for example antioxidants and light stabilizers against polymer degradation or discoloration, also stabilizers against nitrogen oxide yellowing, pigments, for example titanium dioxide or ultramarine blue, dyes, processing aids such as lubricants and abhesives based on alkali or alkaline earth metal stearates, internal release agents based on polydialkylsiloxanes and/or polyether polysiloxanes, and also additives against chlorinated water degradation, for example zinc oxide.
The spinning solutions with a solids content of 20 to 40% by weight, preferably 22 to 30% by weight, based on fiber polymer, and a viscosity of 50 to 350 Paxc2x7s at 25xc2x0 C. are subjected according to the invention to a dry spinning process which may, for example, correspond to the embodiment disclosed in DE Patent 3,534,311.
DE 3,534,311 C2 describes a spinning head for producing elastomer threads, comprising spinning jets with one or more capillaries, feed lines for the liquid material to be spun, a spinning gas supply and distribution system and also a process, especially a dry spinning process, for producing elastomer threads from a spinning solution.
DE 3,534,311 C2 claims a spinning head comprising spinning jets having one or more capillaries, feed lines for the material to be spun, and a spinning gas supply and distribution system, characterized in that the spinning gas supply consists of a central gas pipe and the spinning gas distribution system consists of a cylindrical chamber in which the gas pipe ends; whose diameter is at least three times the diameter of the central gas pipe; whose height is not more than 25% of its diameter; which has a gas-permeable floor with a free area of 2 to 15%; and which, below the central gas pipe, accommodates an impingement plate system consisting of a plurality of overlapping circular rings graded in diameter in a spaced-apart horizontal and concentric arrangement and a circular plate.
The process of the invention makes available splittable elastane multifilament yarns with two to six individual filaments and an overall linear density of 15 to 120 dtex. A preferred embodiment of the process of the invention provides elastane multifilament yarns having two individual filaments and a total linear density of 20 to 50 dtex.
Cooling of the filaments similar to JP 03-059 112 is not relevant for the process of the invention and its purpose. By contrast, however, the herein-described configuration of the spinning jet geometry and the laminarization of the gas flow in the spinning shaft, as described for example in DE Patent 3,534,311, is decisive. This is the only way of ensuring that the extrudate filaments, which are still plastic at the start of the spinning shaft passage, do not come into contact with one another. Whereas JP 03-059 112 describes a kind of aftertreatment, the present invention is directed to the domain of the spinning process (spinning jet and shaft). Hence the present process is simpler in that it does not require the additional step of separate cooling.
The elastane multifilament yarn, wound on a bobbin, can be used in processing techniques in which an individual elastane filament is employed if the multifilament yarn is split into individual filaments before or during processing. Examples of such processing techniques are circular knitting or the manufacture of combination yarn with a core of elastane yarn and an overspun, overblown or overwrapped sheath of nonelastic yarn, for example nylon or cotton. The separation into individual filaments of the elastane multifilament yarns of the present invention takes place between the elastane delivery system and the overspinning, overblowing or overwrapping station. The splitting is effected by simply introducing the separated individual filaments into their respective processing elements and starting the processing operation. If necessary, the process of separation can be further augmented by disposing pins or mandrels upstream of the processing elements.
The elastane multifilament yarns of the invention exhibit high uniformity and an excellent processing behavior and do not differ from conventionally produced elastane yarn spun directly to the final linear density. The splittability, moreover, makes it possible to create, from one spinning station, a multiple of elastane yarn of a certain individual filament linear density corresponding to the number of individual filaments, which considerably increases the efficiency of the manufacturing process, especially the space-time yield. This means that this manufacturing process affords, per unit time, an amount of very fine linear density elastane yarn which is a multiple of that obtained by employing a conventional spinning process leading directly to the final linear density.